Fuel injection pump



Patented May 4, 1954 UNITED STATES ATENT OFFICE Claims priority,application Germany November 22, 1950 11 Claims.

The invention relates to fuel injection pumps. Injection pumps for highspeed internal combustion engines in which the control of the fuelquantity may be coupled with the control of the combustion air, have tosatisfy certain requirements in respect to mechanical features,controllability, kinematics and physical properties. Mechanically, it isnecessary that the drive of the pump plungers is safely operative atvery high speeds and that the mass forces are small. As tocontrollability, it is required that the quantity of fuel delivered bythe pumps is adjustable and can be adapted to the air consumption of theengine at any time throughout the entire ranges of speed and output.Kinematically, the injection process must be controllable, depending onthe prevailing injection law. In order to attain a stable control of thefuel quantities, it is also necessary to prevent or at least greatly toreduce the harmful physical effects of the fuel, such as the formationof steam, gas or air bubbles as well as of cavitations during theprocesses of the fuel inlet and outlet.

Injection pumps of conventional type are suited to fulll the one or theother of the basic requirements. However, none of them is satisfactoryeither from the view point of operation 0r from the View point ofsimplicity of structure.

It is an object of the invention to avoid the drawbacks of theconventional devices and to provide an injection pump which fulfils allor at least most of the mentioned requirements in a compact structurewith simple means and by applying a single control organ.

The invention particularly contemplates the fullment of the requirementsby providing any or all of the following means, viz.: an antifrictionswash plate drive in a fuel injection pump with one or severalcylinders, to operate the plungers and, if so desired, also ancillarypumps, such as a lubrication pump, low pressure fuel pump, etc., therebyavoiding the conventional tappets and rocking levers; an axiallyshiftable slide valve coupled with the pump drive for common rotationand controlling an inlet duct to the pressure chamber of the pump, inorder to adjust the fuel output, in dependence of the R. P. M., by apredeterminable and variable control of a throttle, of the inlet time,and of a maximum fuel quantity; one or several stepwise arranged groovesprovided on the outer surface of the slide valve and which are locatedin the area of the inlet duct along the line of the selected adjustmentpath and may be axially straight or slanting, wedge-shaped or arcuateaclil cording to the required adjustment characteristic, whereby, theinlet angle and the inlet moment can be changed dependent on the axialshift of the slide valve, and the fuel quantity to be injected by thepump will be adjustable dependent on the R. P. M. of the slide valve.

he invention further aims to provide means to adjust the volumetriccapacity of the pressure chamber of the pump at the moment of closing oropening of the inlet duct by either the plunger of the pump or by theslide valve, whereby, the adjustment of the actual highest amount offuel quantity to be ejected by the pump, i. e. injected into the engine,may be rendered approximately constant or variable for the purpose ofadapting that quantity to the ratio of air supplied to the engine in theranges of low R. P. M. and output.

Another object is the provision of a plunger system whereby the pressureof the admeasured quantity of fuel is raised to the injection pressure,and of fuel ducts from the pump to the injection pipe, which ducts arelocated outside of the pressure chamber in order to avoid axial ortransverse bores in the plunger system which might be the cause ofharmful cavities in the pressure chamber.

The invention also contemplates to control the moment of ejection by aring groove or bore which is provided in the body of the plung-er butnot directly connected to the pressure chamber, and to predetermine theejection angle by a throttle at the opening into the injection pipe ofthe engine.

Another object is the provision of means to prevent or reduce theformation of gas, steam, or air bubbles and their harmful eifect on theadjustment of the quantity of the fuel by creating a strong fuelcirculation and rinsing of the suction chamber, and reducing thecapacity of the pressure chamber to practically zero at the end of theejection period.

The invention finally aims to provide a plunger system comprising, foreach injection pump cylinder, a pair of cooperative plungers wherein oneof the plungers is simultaneously operative with one portion in theinjection pump cylinder and with another portion in the cylinder of acirculation pump connected with the injection pump.

Further objects and details of the invention will be apparent from thedescription giv-en hereinafter and the accompanying drawing illustratingan embodiment thereof by way of example. In the drawing Fig. 1 is alongitudinal cross-section, along line I-l of Fig. 2, of a fuel pumpaccording to the invention;

Fig. 2 is a cross-section along line '2.-2 of Fig. l;

Figs. 3 and i are diagrammatical illustrations of the cooperation of theplunger system of the pump with the slide valve in controlling theopening and closing of the fuel inlet duct, Fig. 3 showing part of thepump cylinder in cross-section with plungers therein, and Fig. 4 showinga development of the grooved portion of the slide valve;

Figs. 5 and 6 and Figs. 7 and 8 are views similar to Figs. 3 and 4showing modied slide valve grooves, and illustrate changes of the fuelcontrol in relation to the volumetric capacity of the pressure chamber,and

Fig. 9 is an elevation partly in section of a modified slide valvewithin its bushing approximately in its position of the fuel control forengine idling.

Referring now to the drawing, Figs. l and 2 illustrate a deviceaccording to the invention in which four fuel pumps are combined in onefor charging an engine with four cylinders. However, any other number ofpumps may be similarly combined. The unit comprises a central housingpart lil of substantially circular crosssection. End pieces il and i2are secured thereto by any suitale means, such as for instance thethread i3 to connect the piece l l, and the screw bolts i5; to connectthe piece i2. A gasket 2 is provided between parts lll and l2. Thecentral housing part l is provided with an axial bore i and five boresparallel to the housing axis r--1r:, of which four bores l, l1 I3 and i9are equally spaced from one another, whereas the fifth bore 2S islocated between the bores I8 and i9. The housing parts i8 and l l form acompartment 2i for the accommodation of the driving elements, and intowhich the part l0 projects with a spherical head 22. The drive is of theswash-plate and comprises the plate 23 integral with stub axle 2d whichis journaled in housing part il at 25 and may be coupled by means notshown to a rotating part of the engine for which the pump is destined.The plate 23 has one iti-ce 2E in a plane at right angles to the axis xand another face 21 in a plane aslant thereto. An anti-friction thrustbearing 28 is arranged between the housing part Il and the face 25 andanother similar bearing 2i) is provided between the face 21 and anotherplate 3G which has a central bore 3l with a spherical inner face seatedon the spherical head 22.

The housing part i2 closes an axial chamber 32 in the part iii, andcontains a conduit 33 which opens into chanber 32 and may be connectedto a fuel tank (not shown). Chamber 32 communicates with bore i5. Thepart l2 is furthermore provided on its inner side with four blind boreswhich are co-axial with the bores l5 to i9 respectively and of whichonly the bore 3A is visible in the drawing.

rhe bores l to is contain the cylinders and plungers of the four pumpswhich are alike in every respect. Their detailed description may belimited therefore to the parts accommodated in bore it and theirassociated elements. A bushing 5B is firmly pressed into the bore i8 andextends with its end into a widening l of the bore l5 and with its otherend into the bore 34. A main plunger l is axially shiftable in bushing16. The outer end of the plunger is formed with a collar ft2 and a head43 the latter bearing against the pressure plate 30 of the swash platedrive. A washer |14 engages the collar d2, and a spring d5interpositioned between the washer 44 and the shoulder at the inner endof the widening IB urges the plunger l against the pressure plate 3). Asecond plunger [i5 which in order to distinguish it from the pumpplunger 4l will be hereinafter denoted as the follower plunger, ismovable in the same bore i5 and has an end face 41 adjacent the end facei8 of the pump plunger di. The other end of the follower plunger 46which projects from the bushing 56, has a collar 69 against which acup-shaped washer E!) bears. A spring 5| is inserted between the washer5) and the bottom of the bore 36. Now it will be clear that uponrotation of the axle 20, with swasll plate 23, plunger 4I will rst beaxially shifted against the restraint of spring and then bearing withits face 48 against face Ii'i of the follower plunger fi, will alsoshift the latter against the restraint of the spring 5i. On the returnstroke, the springs i5 and 5l will tend to urge the plungers to followthe pressure plate 3Q which swivels about the center' of the ball head3l. However, whereas plunger (il can follow pressure plate 3? throughthe whole length of the return stroke, plunger `li will be stopped whenflange 98 of cup washer 59 bears against the bottom Si of a recess 92provided in housing lil in continuation of the bore 34 in housing parti2, or when the collar 45 abuts against the end of the bushing 5.

For a purpose to be explained hereinafter, plunger M is provided with anannular groove 52 spaced a substantial distance from its front face 4S.Bushing 4Q is provided with a longitudinal groove 53 communicating atits one end with ring groove 52 through a transverse bore 54 and havingits other end communicating with another transverse bore 55 which endsat the point where the front face 48 of plunger 4| is located when inits outer dead center position illustrated in Fig. l. Bore 55 forms theoutlet port of the pressure chamber of the pump as it will be describedhereinafter. Another transverse bore 56 in bushing d also communicateswith ring groove 52 in the plunger position of Fig. l and extends atright angles with respect to bore 54. The bore 56 which is narrow toform a throttle communicates with a conduit 51 in the housing part It,which constitutes the discharge passage of the pump and may be connectedto the injection pipe of the engine (not shown). There is still anothertransverse bore 58 in bushing dll, which is located intermediate theends of groove 53 but does not communicate with the latter. Bore 58forms the inlet port of the pump.

The major part of the axial bore i5 of housing portion l@ is lined witha bushing Gil within which a cylindrical slide 6l is rotatable andaxially shiftable. The one end of slide 6| extends into an axial bore 52of the axle 24 and is longitudinally slotted at 63 engages a pin 64which traverses the bore 62 of axle 24. Slide 6l is also provided withan axial bore 65 extending a substantial length from the slotted end.Within the bore 65, a spring 55 is located and bears with its one endagainst the aforementioned pin E4, thus tending to shift the slide 6|towards the right hand side in Fig. 1. A rod 61 co-axial with slide 6|is shiftable in a bore 68 provided in the housing l2 and bears with itsone end against the front face 69 of slide 5I and with its other endagainst a control lever 1G pivoted at 1l on a bracket extension l2 ofthe housing part l2. The outer surface of the slide ti is provided witha groove or grooves in general denoted by 80 and extending from thefront face t9 a distance towards the other end of the slide. Thus, thegroove or grooves si? are in permanent communication with chamber 32. Inthe portion of bushing 60 in which the grocved end of the slide ismovable, a transverse bore di is provided which communicates through aduct 82 in housing portion I0 With the aforementioned bore 58 of bushing40. An adjustable throttle of the duct 82 is provided by means of ascrew 83 the head of which extends in the space 32, and the pointed endof which can penetrate into the duct 82 so as to open or close thelatter more or less depending on the setting of the screw 83.

The pump so far described operates in the following manner: Duct 33 isto be connected to a fuel container and the duct 5l to the injectionport of the engine to be charged by the pump. Control lever il! may beeither directly operated by the user or it may be connected with the aircontrol of the engine in order automatically to adjust the ratio of airand fuel charge. Provided the apparatus is in the position of Fig. 1 andthe drive is started to rotate in the direction of the arrow, fuel willenter through the duct 33 and ll the suction chamber 32 of the pump andthe control groove 8@ of the slide E i. In the outer dead centerposition of plunger 4|, both plungers engage each other with their frontfaces il and de, as shown in Fig. l. When, now, the swash plate 23rotates both plungers l and t will move together towards the inner deadcenter position under the action of springs 45 and 5i. The commonmovement continues until flange 5S bears against face Si of the housingand stops the follower plunger 45 whereas plunger di continues itsmovement. The separation of the plungers opens the pressure chamber 96(Fig. 4) of the pump between the front faces of the plungers. Duringthis part of the stroke the face 43 of plunger di passes the bore orport 5S and opens the inlet duct 32. As soon now as groove si? of therotating slide registers with the port 5i fuel will flow from chamber 32through grooves di), port 8|, duct 82 and port 58 into the pressurechamber 96. The chamber will be filled partly or entirely depending onthe duration the connection with chamber 32 is established. Thisduration is determined by the shape of the flanks of groove 3U and theposition and R. P. M. of the slide Si. On the following stroke ofplunger di towards the outer dead center the fuel conned in the pressurechamber 96 will be urged against the front face of 47 of plunger te andsome of the fuel may be forced back to the suction chamber 32. As soonhowever, as port 53 has been closed by the advancing plunger til,plunger it will be caused to take part in the movement against therestraint of spring 5|. When, then, front face el of plunger 46 passesthe port 55, the fuel confined under a pressure which is higher than theejection pressure will enter the longitudinal groove 53 and the ringgroove 52 of plunger il through bore 54. From there the fuel passesthrough the aforementioned throttle bore 56 and can charge the enginethrough the passage 5l. The ejection continues as long as time isrequired to force the fuel through the throttle 56 under the pressure ofspring el bearing on plunger 46 via the cup member 5t. The ejectionperiod is ended when both plungers engage each other with their frontfaces and all fuel has been expelled from the pressure chamber. 'I'helength of the ejection period in degrees of a cycle and the pressure canbe predetermined by a correct selection of pressure of spring 5| inrelation to the cross-section of the throttle bore 56.

The fact that the ducts 55, 53, 54 leading the fuel to the injectionpassage 5l are arranged outside the pressure chamber' et, and that theejection moment is controlled by means of the annular groove 52 ofplunger 4| has essential advantages. On the one hand, the principaleiect of the system of the cooperating pump and follower plungers can befully utilized while simultaneously the formation of harmful cavitiesand of gasand steam bubbles in the pressure chamber Sil is avoided. Onthe other hand the throttle 56 ensures gradually increasing and abruptlystopping ejection kinematics independent from the drive of plunger 4|,and also helps towards a thorough atomization of the fuel.

Means are provided in order to prevent the formation of bubbles of gas,air, steam or foam also in the suction chamber of the pump by thoroughlyflushing that chamber with fuel through circulation between the fueltank and the pump. This is accomplished by designing flange 9! of thespring washer 5! which is in any way required, as a plunger operativeinthe cylinder space 92, 3 so as to constitute a suction and returnpump. For this purpose a passage 93 is provided between the space 92 andthe suction chamber 32, and another passage S34 connects the space S2 toa check valve Q5 from where a return pipe (not shown) may lead to thefuel tank. It will be clear, that the plunger i6 imparts to flange orplunger SE its reciprocating motion so that fuel will be constantlypumped from the tank through chamber 32, pump space @2, valve 95 andback to the tank.

Means are also provided to lubricate the movable parts of the apparatus.Whereas, in the illustrated embodiment four fuel pumps are combined inone unit, only one oil pump is shown. However, it will be clear thatmore than one such pump, may be present. The oil pump is arranged in theaforementioned bore 2e of the housing part l and is of a design similarto that of the fuel pumps. Thus, in a bushing itl?, two plungers IUI and|02 are reciprocable. Plunger ll bears with its head 03 against thepressure plate 3i) of the drive under the action of a spring |54,Plunger ||J2 has a head |65 which can abut against the front face ofbushing Hill, and another spring |06 is interpositioned between head |95and the wall of housing portion I2. The space i6? intermediateA theplungers when they are in the inner dead center position or close to itas shown in Fig. 1, is the pump chamber provided with an inlet duct iwhich may be connected to an oil tank (not shown), and with an outlet|59 which is connected through ducts such as Iii) to the parts to belubricated. A check valve l is in communication with the space H2housing the spring |06, from where the oil may be returned to the tank.The pressure against which the valve li opens is preferably selectedsomewhat higher than the pressure against which the fuel pumps operate.The output of the oil pump is constant and is predetermined by thedistance of the front face of the plunger i632 from the inlet |36 in theinner dead center position. The oil pump may also be used to lubricatethe engine for which the fuel pump is destined.

As stated hereinbefore, it is another object of acca-,sosa

the invention to avoid harmful disturbances of the fuel quantity controland to provide for a. great stability of the control. This can be.attained according to the invention by keeping the now velocity of thefuel in the inlet; to the pres sure chamber S6 as low as. possible inorder to prevent a break of the flow to the pressure chamberparticularly if the fuel is heated. and also to prevent the formation ofcavitations and of strong back pressure waves. For this purpose thegroove Sli is so shaped and arranged that in order to adjust the fuelquantity in the pressure chamber 98 throughout the entire control rangethat angle of a cycle of operation is as large as possible during whichthe inlet. occurs. Furthermore, for the saine purpose, the fuel inletduct 82 is provided with an adjustable throttle in the form of the screw83 although according to experience, it is possible to supply themaximum fuel quantity required at highest R. P. M. over a much smallerinlet angle.

The control of the fuel quantity preferably coupled by means of a cam.or the like (not shown) with the air control of the engine isaccomplished by varying the axial position of the cylindrical slide G i,that means by a shift of lever 'l0 engaging rod 58 against which theslide is urged by spring 66. More or less fuel ows into the pressurechamber 95, depending on the time during which the inlet duct 82 is openwhich time in turn depends on the varying width of the control groove Sas well as onV the position and R. P. M. of the slide 0l. In each axialposition of the slide the fuel quantity decreases with an increase ofthe R. P. M. of the pump and slide, and increases with a decrease of theR. P. M. In order to prevent the fuel quantity from exceeding themaximum amount when the R. P. M. decrease due to a higher load of theinternal combustion engine, and with a View to suiting the quantity ofthe fuel to that of the air charged into the engine in the range of thelower R. P. M., the volumetric capacity of the pressure chamber betweenthe inlet port 58 and the front face 41 of the plunger llt will bepredetermined according to the required fuel-air-ratio. According to theinvention, the eiective volumetric capacity of the pressure chamber canbe rendered approximately constant or variable at the moment of theclosing or opening of the. inlet duct 82 by the plunger lil or by theslide S l.

Figs. 3-8 illustrate diagrammatically three different embodiments fordetermining the volumetric capacity of the pressure chamber in relationto the moments of opening and closing the inlet duct 82, wherein Figs.3, 5, and '7 show the pump plungers and Figs. 4, 6 and 8 aredevelopments of the surfaces of the respectively coordinate slides.

In Figs. 4, and 8, the moments of the opening and of the closing of theinlet duct 82 are entered on the developed slide surfaces by dash linesof which the line o indicates the opening and the line s the closing ofthe duct by plunger 4l. In Figs. 3, 5 and 7, the plunger 4I is shown inits inner dead center position and the dash lines ID in Figs. 4, 5 and 8indicate the points of the slide which register with the center of thepore BI, i. e. the entrance end of the inlet duct 82, when the plungeris in the inner dead center position. The location of the front face 48of plunger 4| in its outer dead center position is indicated by line ODin Fig. 3.

The parts shown in Figs. 3 and 4 fully correspond to those of Fig. 1. Asclearly appearing in let port 58.

Fig. 4, the control. groove SG o1 the slide is tri-v partite, the; partsbeing denoted by 202 and 803 respectively. The tripartite groove isequivalent in its effect to one single groove as the lands between thepartgrooves are actually overlapped by the diameter of the inlet port 5l. This particular form renders it possible to design part grooves witharather pointed taper, which gradually'y register with the port 3i upona shift of the slide, and thus to locate the range of idling and smallloads in the neighborhood of the inner dead center position of theplunger 4l, whereby ther highest regulating effect in dependence oftheR. P. M. will be attained at the highest vacuum inthe pressure chamber96.

In the control pbsition for full load, the groove 801 opens port 8l ofthe inlet duct 82 shortly after the: moment (line o) at which plunger 4lopens port 58.. By an axial displacement of the slide. towards the rightin Fig. 4 the beginning of the fuel inlet will be shifted more and moretowards theA inner dead center owing to the inclination of thecontrolling edge cl.. When moving towards the outer deadcenter, plungeriwill close the inlet ductl before the axially directed trailing controledge b of the groove 8c3 slides across the port 8|. Owing to thisstructure, if the inlet period is long enough, which is possibleprovided the R. P. M. of the slide is small, the entire pressure.chamberV 9G will be nlled with fuel. When, then, the plunger movestowards its outer dead center, excess fuel will be returned through theinlet duct 32 and groove S to the suction chamber 32 until the plungerhas passed the in- The quantity of fuel enclosed between the plungerslll and d5 constitutes the approximately constant, maximum outputquantity which can be attained. However, this quantity is not availableowing 'to the throttling and the short inlet angle in the range of thepoint of the control groove 802, just as it should be at approximatelyidling R. P. M.

The embodiment of Figs. 5 and 5 differs from the foregoing in that thereis an uninterrupted groove 800 having a leading control edge c ofS-curve form and a straight inclined trailing edge d. In this embodimentthe maximum fuel output is variable and is determined by the inclinationof the edge d closing the port 8l at an earlier or later momentdepending on the axial position of the slide. The quantity of fuel whichcan be entrapped between the plunger 1li and plunger 40 at the moment(line s) when plunger 4I closes the port 5B is approximately one half ofthe maximum fuel quantity required in the full load position. Theregulation of the quantity for idling is accomplished in this embodimentshortly before the moment of closing (line s) of the port 58 by plungerdi, and the controlling effect in dependence of the R. P. M. is lesshigh.

In the embodiment of Figs. 7 and 8, means are provided whereby theplunger @li is prevented to follow the drive fully to the inner deadcenter position. In other words there is an interval in which theplunger does not move after a stroke from the outer towards the innerdead center. For this purpose, an abutment Si may be provided againstwhich the plunger can bear, so that it separates from the recedingpressure plate 30 diagrammatically shown in Fig. '7. The groove 00 ofthe slide in Fig. 8 comprises two substantially triangular part grooves80|. and 3%5 with inclined trailing edges.

In this embodiment, the range of control of themaximum fuel quantity isalso variable. Con

trary to the other embodiments the control is accomplished by theinclined control edge c of groove 884 or edge e of groove 8MS closingport 8| at an earlier or later moment figured from the opening of port Bduring the inward stroke of plunger l The volumetric capacity of thepressure chamber during the rest period of plunger 4| corresponds to therequired maximum fuel quantity.

Only a short stroke of plunger di is needed in order to obtain therequired capacity of the pressure chamber, but it is desirable that theinlet angle of the combined grooves 804, 305 is as large as possible.The rest period of the plunger is helpful to that end, as it renders itpossible to apply a sufliciently wide groove, considering the angle fthrough which the slide turns during the period of rest of the plunger.

Now it will be clear that according to the invention, any controlcharacteristic of the maximum fuel quantity can be attained for all loadranges of an internal combustion engine by a suitable formation andarrangement of the control edges d or e of the slide groove in relationto the opening or closing moment of the inlet duct.

It has been stated that in order to be able to apply a large inletangle, it is advisable to throttle the inlet passage of the fuel flow tothe pressure chamber of the pump, for which purpose screw S3 has beenprovided in Fig. 1.

Another means for the same purpose is shown in Fig. 9 where the slide|6| which may be substituted for slide 6| in Fig. 1 has a frontextension |62 of a somewhat reduced diameter. The extension is providedwith a restricted radial bore |63 communicating with an axial bore |54which opens through another radial bore in the groove |80. Thus, fuelcan enter from the chamber 32 through the throttling bore |63 and canpass through groove Ii into inlet duct 82. In this embodiment it isadvisable to apply an undivided groove It. The trailing edge g of thelatter is so located that it controls the port 8| after the moment ofclosing of the inlet duct by the plunger. Edge g may be axially directedor inclined as the edge d in Fig. 6.

It will be apparent to those skilled in the art that many modicationsand alterations of the illustrated structure can be made withoutdeparture from the essence and spiirt of the invention which for thatreason shall not be limited but by the scope of the appended claims.

I claim:

l. In a fuel injection pump, a housing part having an axis and beingformed with a ball head at one of its ends, a pressure plate having acentral spherical cavity engaging said ball head, a swash plateincluding a stub axle co-axial with said housing portion, anantifriction bearing between said swash plate and said pressure plate, aplurality of cylinders formed in said housing, parallel to said axis andequally spaced from one another, a rst plunger in each of saidcylinders, a nrst spring in engagement with the outer end of said iirstplunger so as to urge it against said pressure plate, a second plungerreciprocable in said same cylinder, a second spring connected to saidsecond plunger and tending to urge the latter with its front face inengagement with the front face of said irst plunger, an abutment forsaid second plunger to prevent the latter from following the firstplunger the total length of the stroke of said first plunger under theaction of said second spring so as to form a pump chamber in saidcylinder when said plungers sepa.- rate, a control organ rotatable in anaxial bore of said housing portion, a fuel inlet duct for each cylinderforming a port in said pump chamber under the control of the coordinateiirst plunger, the other ends of said ducts being under the control ofsaid control organ, said control organ communicating with a fuel sourceso as to admit fuel to said inlet ducts, one after the other, uponrotation of said axle.

2. A fuel injection pump as claimed in claim 1, further comprising a,lubricating pump arranged in said housing between two adjacent ones oi!said cylinders and including a plunger in operative connection with saidpressure plate, and oil ducts between said lubricating pump and saidcylinders.

3. In a fuel injection pump the combination of a cylinder, a rst plungerreciprocable therein, a rotary drive including means to reciprocate saidplunger, a second plunger reciprocable in said cylinder and adapted toengage said rst plunger in a face to face relationship, a spring bearingon said second plunger and'urgingft towards said iirst plunger, anabutment for said second plunger to prevent the latter from followingsaid rst plunger the total length of the stroke of said first plunger inthe direction of the force of said spring so as to form a pump chamberin said cylinder when said plungers separate, a fuel inlet duct forminga port in said chamber under the control of said first plunger, a rotarycon'- trol organ coupled with said drive and controlling liow throughsaid duct at a point of the latter other than said port, and a two partdischarge duct provided in the cylinder wall, the rst part beingarranged substantially parallel to the cylinder and forming with its oneend a discharge port of said chamber under the control of said secondplunger, the other end of said rst part of said discharge duct forming athird port in said cylinder between said chamber and said drive andbeing under the control of the edges of an annular groove provided onsaid rst plunger, the other part of said discharge duct opening with oneof its ends towards the outside and forming with its other end a fourthport peripherally spaced from said third port but at substantially thesame axial distance from said chamber as said third port.

4. A fuel injection pump as claimed in claim 3, wherein said fourth portconstitutes a throttle.

5. In a fuel injection pump a housing including a cylinder, a rstpositively driven plunger reciprocable in said cylinder, a secondplunger in said cylinder in a face to face relationship to the iirstplunger and extending with its end from said cylinder, said plunger endembodying a third plunger reciprocable in a cylindrical space providedin said housing coaxial with said cylinder, a spring between said thirdplunger and the bottom of said space to urge said second plunger intoengagement with said rst plunger, said third plunger being adapted toabut against a portion of said housing to prevent said second plungerfrom following said first plunger the total length of the stroke of thelatter thereby to open a pressure chamber between the idrst and thesecond plunger, a suction chamber in said housing and adapted to beconnected to a fuel source, an inlet duct from said suction chamber tosaid pressure chamber, a discharge duct connected to said pressurechamber for delivery of fuel to an engine, both said ducts being underthe control of said rst plunger, an

-11 inlet `,connection between said suction chamber and said cylindricalspace under the control of ysaid third piston, an outlet duct from saidspace,

and a check valve `in said outlet duct.

6. In a fuel injection pump, the combination of .a housing, a iirstcylinder and a second cylinder in said housing, a first plungerreciprocable in said first cylinder, a rotary drive including means toreciprocate said plunger, a second plunger reciprocable in said firstcylinder and adapted to engage said first plunger in a face to facerelationship, a spring bearing on said second plunger and urging ittowards said first plunger, an abutment `for said second plunger toprevent the latter from following said first plunger the total length ofthe an inlet port in said chamber under the control -of said rstplunger, and having its other end in another port of said secondcylinder, a cylindrical slide coupled with one of its endg to said driveso as to be rotatable and .axially shiftable in said second cylinder, atleast one groove provided in lthe surface of said slide and extendingfrom the free end towards the other end of said slide a distancesubstantially the distance said slide i5 axially shiftable, the edges ofsaid groove being in controlling relationship to said other port, meansto -establish communication of said groove with a `fuel source, andoperative means to shift said slide in the axial direction.

7. A fuel injection pump as claimed in claim 6, wherein the groove edge'leading upon rotation of said slide is rearwardly inclined from thefree end of the slide, and the trailing edge is axially directed, thedrive being so connected to said first plunger and said slide rand theparts being so arranged that the leading edge opens said other vportafter the iirst plunger opens said inlet port, yand that said trailingedge closes said other port after the closing of said inlet port.

8. A fuel pump as `claimed in claim 6, wherein said leading groove edgeis rearwardly curved in an S-shape, and said trailing edge is rearwardlyinclined.

9. A fuel pump as claimed in claim 6, wherein the leading edge of saidgroove is axially directed and the trailing edge is forwardly inclinedfrom its opentowards its closed end.

10. A fuel pump as claimed -in claim 6, wherein another spring isincluded in said means to reciprocate said first plunger and connectedto the latter so as to urge said plunger into engagement with saiddrive, a `second abutment ymeans connected with said first plunger toprevent said first plunger from following said drive under the action ofsaid other spring before the end of the retreating stroke of said drive,so as to cause an interval during which said iirst plunger does notmove, the edge of said slide groove leading when said slide rotatesbeing axially directed, and the trailing edge vbeing forwardly inclinedfrom the free end of said slide.

11. A fuel 'injection pump as claimed in `claim 6, said groove beingdivided in several parts, lthe lands between the groove `parts extendingin a direction from the free end of said slide towards its other end andbeing of a Width smaller than the diameter of said other port, and atleast one of said part grooves being sharply pointed.

References 'Cited inthe le 0f this patent UNITED STATES PATENTS NumberName Date 2,142,086 Alden Jan. 3, 1939 2,261,471 I-Iull Nov. 4, 19412,268,000 Treer Dec. 30, 1941 2,573,792 Jakobsen Nov. 6, 1951 FOREIGNPATENTS Number Country Date 508,730 Germany 1930

